Apparatus for picking up and feeding individual sheets from a stack of sheets

ABSTRACT

The apparatus comprises a rotating suction roller which removes sheets from the bottom of a stack of sheets and carries them individually to the delivery roller of a printing or duplicating machine. A gripping device provided on the periphery of the delivery roller is equipped with a stop, against which an edge of the sheet is pushed by virtue of the relative movement between the delivery roller and the suction roller. The slight compression of the sheet against the stop ensures correct positioning of the sheet on the delivery roller, which position is maintained by means of the gripping device.

United States Patent .lahme Jan. 21, 1975 [76] Inventor: Hans Joachim Jahme,

Eckernfordestrasse 1, Wiesbaden, Germany 22 Filed: Mar. 26, 1973 21 Appl. No.: 344,556

[30] Foreign Application Priority Data Oct. 20, 1972 Germany 2252302 [56] References Cited UNITED STATES PATENTS 3,536,321 10/1970 Straube 271/53 Vite ..271/95 FOREIGN PATENTS OR APPLICATIONS 1,084,737 12/1960 Germany 271/11 Primary ExaminerEvon C. Blunk Assistant Examiner-Bruce H. Stoner, Jr. Attorney, Agent, or Firm-Wenderoth, Lind & Ponack [57] ABSTRACT The apparatus comprises a rotating suction roller which removes sheets from the bottom of a stack of sheets and carries them individually to the delivery roller of a printing or duplicating machine. A gripping device provided on the periphery of the delivery roller is equipped with a stop, against which an edge of the sheet is pushed by virtue of the relative movement between the delivery roller and the suction roller. The slight compression of the sheet against the stop ensures correct positioning of the sheet on the delivery roller, which position is maintained by means of the gripping device.

3 Claims, 4 Drawing Figures APPARATUS FOR PICKI NG UP AND FEEDING INDIVIDUAL SHEETS FROM A STACK OF SHEETS BACKGROUND OF THE INVENTION The present invention relates to an apparatus for picking up and feeding individual sheets from a stack of sheets. The invention is particularly useful for the picking up and feeding of sheets of paper in printing and duplicating machines.

In offset and duplicating machines of conventional design, and particularly in offset printing machines designed for the printing of sheets of approximately A3 size and smaller, the sheets are picked up from the top of a stack by means of suction elements, preferably suction pads fitted on a rod, and, by a cam-controlled movement of the suction-pad rod, are passed into the zone of a number of gripping devices of a roller, which gripping devices seize the sheets and draw them into the machine after they have been released by the suction pads. In this method it is necessary briefly to increase the speed of movement of the suction-pad rod from zero (pick-up of the sheet from the stack by suction) to more than the peripheral speed of the rollers (delivery of the sheet to the zone of the gripping devices), after which the speed is immediately reduced to zero again (placing of the sheet in readiness for it to be seized by the gripping devices, i.e., aligning of the sheet) Since with these constructions, the sheet is hanging from the suction pads when it is moved and in an extremely short period passes from the practically stationary condition to a high speed of movement, a maximum printing speed is imposed on the machine, this speed being limited by, the factors involved in the placement of the sheet in this design of equipment, whereas the speed of revolution of all the rollers could be increased.

It is also known practice to use friction for placement of the sheets, especially in offset printing and duplicating machines for handling small sheet sizes. In these machines a cam-controlled friction member is applied to the stack and this pushes the top sheet from the stack into the machine. The printing speed that can be achieved when these sheet-positioning devices are used is even less than when suction elements are employed, since the sheets adhere less firmly to the friction members. Furthermore there is a very high risk of several sheets being picked up and moved simultaneously, which disadvantage is largely avoided in the case of suction sheet-feeding means by directing a stream of compressed air onto the forward edge of the stack.

German Pat. Spec. No. 1,084,737 describes an apparatus for picking up and feeding blank sheets, in particular labels, which apparatus has a particularly high pick-up speed. In the arrangement described in this Patent Specification, the sheet is seized from the bottom of a stack by a suction pick-up roller and, while this roller is moving towards the end of the sheet and is rotating, the sheet is passed around the roller until it is seized by a delivery roller and pulled away from beneath the stack, while the suction pick-up roller is moving back to its original position to pick up the next sheet.

The sheets are held on the delivery roller by means of a vacuum which can be applied to the sheets through passages in the delivery roller, and which can be maintained or relaxed depending upon the angular position of the delivery roller.

This arrangement which is particularly useful for the labelling of cylindrical bodies, especially bottles, cannot be applied to offset printing and duplicating machines, since, when the sheets are passed to the delivery roller there is no guarantee that they will be accurately positioned in the manner required in offset printing and duplicating machines, i.e., the precise positioning of the sheet on the periphery of the delivery roller and thus the position of the printed image on the sheet are largely a matter of chance. The labelling of cylindrical bodies does not call for great precision in the placement of the labels, since the position at which the label is applied is of no great importance.

SUMMARY OF THE INVENTION The present invention seeks to effect a rapid transfer such as is achieved in the apparatus of German Pat. Spec. No. 1,084,737 in the case of offset printing and duplicating machines.

According to the invention there is provided an apparatus for picking up and feeding individual sheets from a stack of sheets, such apparatus including a rotatable delivery roller, a rotatable pick-up roller having a plurality of radially directed suction passages disposed along a generator thereof for engaging the bottom sheet of the stack of sheets at a point adjacent an edge thereof and feeding the sheet to the delivery roll, and means for swinging the axis of rotation of the pick-up roller backwards and forwards about the axis of rotation of the delivery roller. The arrangement is such that, at the instant the pick-up roller engages the bottom sheet during use of the apparatus, the axis of rotation of the pick-up roller is moving in the same direction as the delivery roller. At least one gripping device is provided on the periphery of the delivery roller for holding the sheet being fed thereto. Stop means are provided on the gripping device for locating the leading edge of the sheet being fed into the gripping device by the pick-up roller and against which, during use of the apparatus, such edge of the sheet is pushed under a compressive bias by the pick up-roller.

By means of this apparatus, the forward edge of each sheet can be moved into the open gripping device on the delivery roller and against the stop means for the purpose of achieving accurate placement, and at the same time compensating for faulty positioning of shee in the stack container.

The or each gripping device is preferably fitted on the periphery of the delivery roller and pivots about a spindle extending parallel with the generator of the delivery roller upon actuation by a cam control mechanism. The cam control mechanism is so designed that the gripping device of the delivery roller closes when the forward edge of sheet has reached the stop means in the open gripping device.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be better understood, an embodiment thereof will now be described by way of example only and with reference to the accompanying drawings in which:-

FIG. 1 is a general view of the apparatus for picking up and feeding stacked blank sheets;

FIG. 2 shows the apparatus in the position in which pick-up by suction is taking place;

FIG. 3 shows the apparatus in the transfer position, the gripping device being open; and

FIG. 4 is a view, on a larger scale, of a portion of the apparatus illustrated in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows the different positions that the apparatus of the invention can occupy. Rotation of a crank disc 1 causes a pick-up or suction roller to be moved backwards and forwards over the periphery of a delivery roller 7, by way of a connecting rod 3 and a rocker 4, rocker 4 being pivoted about the rotational axis of delivery roller 7. The suction roller 5 is caused to move over the delivery roller 7 in a positive rolling movement by means of toothed wheels (not illustrated) fitted between the suction roller and the delivery roller. The crank disc 1 and the delivery roller 7 are driven in the same direction by means of toothed belts, chains or the like.

In order to clearly explain the operation of the apparatus, some of the various positions of the mechanism are shown in FIG. 1 and indicated by the letters S, U, rT and IT. In the position S, the suction roller 5 is in the sheet pick-up position and a vacuum is applied through the passage 8 in the suction roller and through a plurality of radially directed passages 9 disposed along a generator of the peripheral surface of the suction roller to pick up the bottom sheet from a stack 10 of sheets. The mechanism is arranged so that, during the period during which each sheet is picked off the bottom of stack 10, the speed at which the suction roller moves over the delivery roller is equal to one half the peripheral speed of the delivery roller. When the point U is reached, the forward edge of the sheet is introduced into a number of open grippers 6 on the delivery roller, which grippers close when the forward edge of the sheet has reached a stop 12, the vacuum at the same time being cut off. The apparatus then passes through the positions r and IT, and picks up the next sheet at the position S.

FIG. 2 shows the apparatus of the invention for picking up and feeding stacked blank sheets in the sheet pick-up position designated by the letter S in FIG. 1. The sheet to be picked up is not seized directly at its edge but at a point which is offset inwardly through a certain distance, so that the edge of the picked up sheet extends tangentially beyond the suction roller.

When the suction roller 5 is moved by rocker 4 in a counterclockwise direction around delivery roller 7 and the delivery roller 7 is rotated in the same direc' tion, the apparatus reaches the transfer position shown in FIG. 3 in which the grippers 6 are open, so that that portion of the picked up sheet that projects tangentially beyond the suction roll 5 can be inserted into the grippers. As can be seen more clearly from the portion shown on a larger scale in FIG. 4, each gripper 6 is at the point in time located forwardly of the point of contact between the suction and delivery rollers taken in the direction of rotation of the delivery roller, at the moment at which the sheet is being transferred to the delivery roll, at which point of contact the passages 8 in the suction roller are located at that moment. Also, at this moment the distance between the passage 8 in the suction roller and the stop 12 on the gripper 6 of the delivery roller must be somewhat less than the length of the end portion of the picked up sheet extending tangentially beyond the suction roller. Because of this, when the forward edge of the sheet is pushed against the stop or stops 12, the sheet curves slightly upwards by an amount depending upon the oversize on length (see FIG. 4). This curvature represents the extent to which it is possible to compensate for errors in the distance between the forward edge of the sheet and the stops when positioning the sheet. The sheet is therefore moved against the stop or stops under a compressive bias. This ensures that the forward edge of the sheet 13 is firmly applied to the stop 12 so that correct placement of the sheet to be printed upon, and therefore a precisely predictable position of the printed image on the sheet, is always achieved. Without the above-described curvature when pushing the sheets against the stops, errors in the position of the sheets, for example caused by faulty stacking of the sheets in the stack container, could not be compensated.

After the forward edge of the sheet has thus been aligned on the stop 12, the grippers 6 of the delivery roller close against a backing element 11, so that the sheet 13 is held firmly between the backing element l1 and the grippers 6 of the delivery roller.

The grippers 6 on the delivery roller are mounted on a spindle 14 which ia disposed at the periphery of the delivery roller and parallel with one of its generators. The grippers can be spring-biased towards the closed position, whereas the spindle 14, mounted at the endfaces of the delivery roller, is acted upon through levers by a cam-control mechanism which causes the grippers to open and close in dependence upon the angular position of the delivery roller. The cam-control mechanism for the grippers on the delivery roller is not illustrated in the drawings.

A plurality of grippers are distributed along the spindle 14 over the width of the delivery roller, so that the sheet is held in a uniform manner over its entire width. To enable the suction roller 5 to roll over the opened grippers 6, annular channels are formed at the appropriate places on the suction roller as indicated at 15 in FIG. 4.

I claim;

1. An apparatus for picking up and feeding individual sheets from a stack of sheets, said apparatus comprismg:

a rotatable delivery roller;

a pick-up roller mounted about the periphery of said delivery roller, said pick-up roller being rotatable about an axis of rotation thereof, said pick-up roller having therein a plurality of radially directed suction passages opening onto the peripheral surface of said pick-up roller along a line forming a generator of said peripheral surface of said pick-up roller;

at least one gripping device means provided on the periphery of said delivery roller for receiving and gripping a sheet being fed thereto by said pick-up roller;

means, while said pick-up roller and said delivery roller and rotating about the respective axes of rotation thereof, for swinging the axis of rotation of said pick-up roller backwards and forwards about the axis of rotation of said delivery roller over a plurality of positions about the periphery of said delivery roller including a first position whereat said suction passages and directed at the lowermost sheet of a stack of sheets at points spaced from an edge of said lowermost sheet by a first distance, to

2. An apparatus as claimed in claim 1, further comprising a spindle pivotally mounting said gripping device means on said delivery roller and extending parallel to said axis of rotation of said delivery roller.

3. An apparatus as claimed in claim 1, wherein said means for swinging moves said pick-up roller, when at said first position, at a speed equal to one-half the peripheral speed of said delivery roller. 

1. An apparatus for picking up and feeding individual sheets from a stack of sheets, said apparatus comprising: a rotatable delivery roller; a pick-up roller mounted about the periphery of said delivery roller, said pick-up roller being rotatable about an axis of rotation thereof, said pick-up roller having therein a plurality of radially directed suction passages opening onto the peripheral surface of said pick-up roller along a line forming a generator of said peripheral surface of said pick-up roller; at least one gripping device means provided on the periphery of said delivery roller for receiving and gripping a sheet being fed thereto by said pick-up roller; means, while said pick-up roller and said delivery roller and rotating about the respective axes of rotation thereof, for swinging the axis of rotation of said pick-up roller backwards and forwards about the axis of rotation of said delivery roller over a plurality of positions about the periphery of said delivery roller including a first position whereat said suction passages and directed at the lowermost sheet of a stack of sheets at points spaced from an edge of said lowermost sheet by a first distance, to a second position whereat said suction passages are directed at said delivery roller at points on the periphery thereof spaced from said gripping device means by a second distance less than said first distance; and each of said gripping device means having thereon stop means for abutting said edge of said lowermost sheet and exerting compressive stress thereon when said pick-up roller is in said second position.
 2. An apparatus as claimed in claim 1, further comprising a spindle pivotally mounting said gripping device means on said delivery roller and extending parallel to said axis of rotation of said delivery roller.
 3. An apparatus as claimed in claim 1, wherein said means for swinging moves said pick-up roller, when at said first position, at a speed equal to one-half the peripheral speed of said delivery roller. 